(a) Field of the Invention
The present invention relates to a piezoelectric actuator having an array of drive columns and, more particularly, to a piezoelectric actuator that is especially suitable for ink jet printers, that can be fabricated with improved positional accuracy and increased integration density, and that can be stably driven. The present invention also relates a method for fabricating such a piezoelectric actuator.
(b) Description of the Related Art
In ink jet printers, a piezoelectric actuator is generally used in the ink jet head of the ink jet printers for ejecting liquid ink therefrom. A conventional piezoelectric actuator for such an ink jet head is proposed in, for example, Patent Publication No. JP-A-96-156272. FIGS. 1A and 1B show the proposed piezoelectric actuator.
For fabrication of the piezoelectric actuator, a plurality of elongate piezoelectric plates 88 of a stacked structure are first bonded onto a substrate 84 along electrode plates 86 and 87 formed thereon, as shown in FIG. 1A.
Subsequently, a plurality of slits extending in a direction perpendicular to the longitudinal direction of the elongate piezoelectric plates 88 are formed in the piezoelectric plates 88 and on the surface portion of the substrate 84 at a predetermined pitch. Thus, a plurality of rows 91 are formed each having a plurality of stacked piezoelectric elements (or drive columns) 89 and 90. Subsequently, the electrode plates 86 and 87 are subjected to patterning to form a plurality of external signal electrodes 93 each corresponding to one of the piezoelectric elements 89, as shown in FIG. 1B.
Surface electrodes are then provided on the opposite side surfaces of each of the piezoelectric elements 89 and 90. The piezoelectric element has therein a plurality of layered internal electrode films including a plurality of signal electrodes and a plurality of common electrodes alternately disposed with each other. Each surface electrode of the piezoelectric elements connects the signal electrodes or common electrodes together. The surface electrode connecting the internal common electrodes together is connected via conductive material to an external common electrode 82 formed on the substrate 84, whereas the surface electrode connecting the internal signal electrodes together is connected via conductive material to an external signal electrode 93 formed on the substrate 84. Further, a support member 94 is disposed on and bonded to the substrate 84, the support member 94 having an opening for encircling each row of the piezoelectric elements 89 and 90 so that the top surface of the support member 94 is flush with the top surfaces of the piezoelectric elements 89 and 90. Each of the stacked piezoelectric elements 89 and 90 has a displacement output surface at the top thereof far from the substrate 84, and, due to the longitudinal piezoelectric effect, outputs a displacement in the same direction as the direction of the stacking.
In the conventional technique as described above, a plurality of piezoelectric elements are obtained after separation of the elongate piezoelectric plate by using slits extending in the transverse direction of the elongate piezoelectric plate. Thus, each piezoelectric element has a rectangular planar shape, and an ink chamber and a nozzle for ejecting liquid ink in association with the piezoelectric element should conform to the rectangular shape of the piezoelectric element. A pattern of external electrodes for each row of the piezoelectric elements is located on either side of the piezoelectric plates. This prevents a higher integration of the actuator unit, such as provision of three or more rows of piezoelectric elements on a single actuator unit, resulting in a difficulty in increasing the number of nozzles per unit area, as well as in a low productivity.
Further, since the material of the substrate differs from that of the piezoelectric element, it generates differences in the thermal expansion coefficient and in workability between the substrate and the piezoelectric element during machining of the slits.
Furthermore, a bonding process must be performed twice; i.e., when the piezoelectric plate is bonded onto the substrate and when the support member is bonded onto the substrate. In addition, when the piezoelectric plates are positioned relative to the external electrode patterns on the substrate before being bonded to the substrate, a positional deviation is often caused between the piezoelectric plates.